Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/1039—Polymeric electrolyte materials halogenated, e.g. sulfonated polyvinylidene fluorides
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
  • H01M8/1025—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having only carbon and oxygen, e.g. polyethers, sulfonated polyetheretherketones [S-PEEK], sulfonated polysaccharides, sulfonated celluloses or sulfonated polyesters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/1041—Polymer electrolyte composites, mixtures or blends
  • H01M8/1046—Mixtures of at least one polymer and at least one additive
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0065—Solid electrolytes
  • H01M2300/0082—Organic polymers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
  • H01M4/8803—Supports for the deposition of the catalytic active composition
  • H01M4/881—Electrolytic membranes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the present invention relates to a polymer electrolyte membrane for a polymer electrolyte fuel cell, whereby the initial output voltage is high, and the high output voltage can be obtained over a long period of time, and a membrane-electrode assembly having the polymer electrolyte membrane.
• a fuel cell is a cell whereby a reaction energy of a gas as a feed material is converted directly to electric energy, and a hydrogen-oxygen fuel cell presents no substantial effect to the global environment since its reaction product is only water in principle.
• a polymer electrolyte fuel cell employing a polymer electrolyte membrane as an electrolyte membrane can be operated at room temperature to provide a high power density, as a polymer electrolyte membrane having high ion conductivity has been developed, and thus is expected to be a prospective power source for mobile vehicles such as electric cars or for small cogeneration systems, along with an increasing social demand for an energy or global environmental problem in recent years.
• a proton conductive ion exchange membrane is commonly employed as a polymer electrolyte membrane, and an ion exchange membrane made of a perfluorocarbon polymer having sulfonic acid groups, is particularly excellent in the basic properties.
• gas diffusion type electrode layers are disposed on both sides of the ion exchange membrane, and power generation is carried out by supplying a gas containing hydrogen as a fuel and a gas (such as air) containing oxygen as an oxidizing agent to the anode and the cathode, respectively.
• the reaction proceeds via hydrogen peroxide (H 2 O 2 ), and it is concerned that the electrolyte membrane may be deteriorated by the hydrogen peroxide or peroxide radicals to be formed in the electrode layer. Further, to the anode, oxygen molecules will come from the cathode through the membrane, and it is concerned that hydrogen peroxide or peroxide radicals may be formed at the anode too. Especially when a hydrocarbon polymer membrane is used as the polymer electrolyte membrane, it is poor in the stability against radicals, which used to be a serious problem in an operation for a long period of time.
• a perfluorocarbon polymer having sulfonic acid groups as a polymer remarkably excellent in the stability against radicals has been known.
• a polymer electrolyte fuel cell employing an ion exchange membrane made of such a perfluorocarbon polymer is expected as a power source for e.g. automobiles or housing markets, and a demand for its practical use is increasing, and its developments are accelerated. In such applications, its operation with particularly high efficiency is required. Accordingly, its operation at higher voltage is desired, and at the same time, cost reduction is desired. Further, from the viewpoint of the efficiency of the entire fuel cell system, an operation under low or no humidification is required in many cases.
• Non-Patent Document 1 it is considered that, also in the case of the ion exchange membrane made of a perfluorocarbon polymer having sulfonic acid groups, deterioration of the electrolyte membrane proceeds due to hydrogen peroxide or peroxide radicals in operation under low or no humidification.
• the present invention provides the following polymer electrolyte membrane and the following membrane-electrode assembly using the membrane.
• a polymer electrolyte membrane which comprises a polymer electrolyte having sulfonic acid groups, and contains any one of the following (a) to (c):
• a membrane-electrode assembly for a fuel cell which comprises a layer of the above polymer electrolyte membrane, and a catalyst layer containing a catalyst, an electrically conductive material and an ion exchange resin, provided on both sides of the polymer electrolyte membrane.
• a polymer electrolyte fuel cell provided with a membrane-electrode assembly having the polymer electrolyte membrane of the present invention is excellent in durability and capable of generating the electric power stably over a long period of time.
• the present invention is characterized in that the polymer electrolyte membrane contains any one of the above (a) to (c). That is, it is characterized in that the polymer electrolyte membrane contains both cerium ions and the above organic compound (X), contains the above inclusion compound (Y), or contains at least one of cerium ions and the organic compound (X), and the above inclusion compound (Y). It is unclear whether cerium ions and the organic compound (X) completely form the inclusion compound, whether they merely coexist, or whether they undergo equilibrium reaction of inclusion/dissociation in the membrane. However, it is estimated that the presence of them in the membrane effectively improves resistance of the electrolyte membrane to hydrogen peroxide or peroxide radicals.
• the cerium ions present in the membrane or the inclusion compound (Y) may be trivalent or tetravalent, and the inclusion compound (Y) may also be trivalent or tetravalent.
• an inclusion compound is one type of an addition compound comprising a lattice structure of one type of molecules and other atoms or molecules regularly trapped in a certain proportion in the lattice structure.
• the lattice structure may have any of the cage shape, the cylinder shape and the layer shape, and particularly an inclusion compound in the cage shape is sometimes called a clathrate compound ( edited by Shoji Shida, Morikita Publishing Co., Ltd., 1981, first edition, page 1,518 ).
• the organic compound forming an inclusion compound may, for example, be a calixarene (cyclophane), a crown ether or a cyclodextrin.
• the organic compound (X) capable of forming an inclusion compound with cerium ions is preferably a crown ether.
• the crown ether means a crown ether and its derivative having a crown ether structure. Specifically, it may, for example, be a crown ether such as 12-crown-4,15-crown-5 or 18-crown-6, a crown ether derivative such as dibenzo-18-crown-6, dicyclohexano-18-crown-6 or (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid, or a crown ether other than the above, such as a lariat crown ether having a long chain or a cryptand which is a bicyclic crown.
• Such a crown ether is a compound having a ring with a repeating structure of (-CH 2 -CH 2 -Y-) units, and Y is a hetero atom such as O, S, N or P.
• Y is a hetero atom such as O, S, N or P.
• Such a compound has a capability of trapping cations such as metal ions in the ring and forming an inclusion compound.
• 15-crown-5 or 18-crown-6 is used, and such a crown ether is preferred since cerium ions are easily trapped therein in view of the size of the cerium ions.
• the above (a) to (c) may be present in any state in the electrolyte membrane, and they are not necessarily present uniformly in the electrolyte membrane.
• the above (a) to (c) may be present with a concentration gradient in the thickness direction of the polymer electrolyte membrane, or a layer containing none of the above (a) to (c) may be present in a multilayer structure polymer electrolyte membrane. Therefore, in a case where it is required to increase durability against hydrogen peroxide or peroxide radicals particularly on the anode side, the above (a) to (c) may be contained in the vicinity of the surface to be in contact with the anode at a high concentration or may be contained only in a layer closest to the anode.
• a method to obtain the polymer electrolyte membrane of the present invention is not particularly limited, and the following methods may, for example, be mentioned.
• the cerium ions may be trivalent or tetravalent, and various cerium salts are used to obtain a solution containing cerium ions.
• a salt containing trivalent cerium ion include cerium(III) acetate (Ce(CH 3 COO) 3 ⁇ H 2 O), cerium(III) chloride (CeCl 3 ⁇ 6H 2 O), cerium(III) nitrate (Ce(NO 3 ) 3 ⁇ 6H 2 O) and cerium(III) sulfate (Ce 2 (SO 4 ) 3 ⁇ 8H 2 O).
• a salt containing tetravalent cerium ion examples include cerium(IV) sulfate (Ce(SO 4 ) 2 ⁇ 4H 2 O), cerium(IV) diammonium nitrate (Ce(NH 4 ) 2 (NO 3 ) 6 ) and cerium(IV) tetraammonium nitrate (Ce(NH 4 ) 4 (NO 3 ) ⁇ 4H 2 O).
• examples of an organic metal complex salt of cerium include cerium(III) acetylacetonate (Ce(CH 3 COCHCOCH 3 ) 3 ⁇ 3H 2 O).
• the inclusion compound (Y) formed by reaction of cerium ions with the crown ether will be represented as a cerium/crown ether inclusion compound or (Ce/Crown) n+ .
• cerium/crown ether inclusion compound is a trivalent
• the cerium/crown ether inclusion compound or (Ce/Crown) 3+ is bonded to three -SO 3 - as shown below:
• the polymer electrolyte membrane of the present invention has excellent resistance to hydrogen peroxide or peroxide radicals.
• the reason is not necessarily clear, but it is estimated as follows.
• the electrolyte membrane containing cerium ions and the organic compound (X) at least part of them form the inclusion compound (Y), which interacts with sulfonic acid groups (-SO 3 - ), whereby part of the sulfonic acid groups are ion-exchanged with the inclusion compound (Y) to form the above structure, thus effectively improving resistance of the polymer electrolyte membrane to hydrogen peroxide or hydrogen radicals.
• a preliminarily produced inclusion compound (Y) is incorporated in the electrolyte membrane.
• the polymer electrolyte membrane contains cerium ions and the organic compound (X) in a total amount of preferably from 0.5 to 80 mass% based on the polymer electrolyte membrane.
• the inclusion compound (Y) is regarded as a mixture of them. That is, in a case where cerium ions and the organic compound (X) are separately or as a mere mixture are blended in the polymer electrolyte, the amount of the inclusion compound (Y) is not considered even if it is formed in the polymer electrolyte, and only the total amount of cerium ions and the organic compound (X) blended is calculated.
• the amount of the inclusion compound (Y) is considered as the total amount of cerium ions and the organic compound (X) forming the inclusion compound (Y). Further, in a case where cerium ions and the organic compound (X) not forming the inclusion compound (Y) are present in addition to cerium ions and the organic compound (X) forming the inclusion compound (Y), their amounts are also calculated.
• the total content of cerium ions and the organic compound (X) is more preferably from 1 to 60 mass%, furthermore preferably from 2 to 50 mass%. If the total content of cerium ions and the organic compound (X) is lower than the above range, no sufficient stability against hydrogen peroxide or peroxide radicals may be secured. Further, if the total content of cerium ions and the organic compound (X) is higher than the above range, no sufficient electrical conductivity of hydrogen ions may be secured, thus increasing the membrane resistance to lower power generation properties.
• the relative ratio of the organic compound (X) to cerium ions contained in the polymer electrolyte membrane is preferably such that the amount of the organic compound (X) is from 0.2 to 1.2 mole per mole of cerium ions.
• the inclusion compound (Y) is regarded as a mixture of them.
• the inclusion compound (Y) is usually a reaction product of one cerium ion with one molecule of the organic compound (X). Therefore, in a case where the amount of the organic compound (X) is not 1 mole per mole of cerium ions, it is considered that either cerium ions or the organic compound (X) in an excessive amount is contained in the polymer electrolyte membrane without forming the inclusion compound (Y).
• cerium ions and the organic compound (X) in the polymer electrolyte membrane form the inclusion compound (Y) in fact.
• the polymer electrolyte having sulfonic acid groups before incorporation of any one of the above (a) to (c) is not particularly limited, but its ion exchange capacity is preferably from 0.5 to 3.0 meq/g dry resin, particularly preferably from 0.7 to 2.5 meq/g dry resin. If the ion exchange capacity is less than 0.5 meq/g dry resin, no satisfactory conductivity of ions will be secured, and if the ion exchange capacity exceeds 3.0 meq/g dry resin, the polymer electrolyte will be gelated, and it can not be formed into a membrane.
• the ion exchange capacity is particularly preferably from 1.0 to 2.5 meq/g dry resin.
• the polymer electrolyte is preferably a fluoropolymer, particularly preferably a perfluorocarbon polymer (which may contain an etheric oxygen atom).
• the polymer electrolyte is preferably a sulfonic acid group-containing perfluorocarbon polymer.
• the perfluorocarbon polymer is not particularly limited but is preferably a perfluorocarbon polymer having a sulfonic acid group-containing side chain represented by -(OCF 2 CFX) m -O p -(CF 2 ) n -SO 3 H (wherein m is an integer of from 0 to 3, n is an integer of from 1 to 12, p is 0 or 1, and X is a fluorine atom or a trifluoromethyl group).
• the sulfonic acid group-containing perfluorocarbon polymer is obtained usually by copolymerizing a perfluorovinyl compound having a -SO 2 F group and another perfluorovinyl compound to produce a copolymer having -SO 2 F groups, and converting the -SO 2 F groups in the copolymer to sulfonic acid groups.
• perfluorovinyl compound examples include compounds represented by the following formulae (i) to (iii).
• q is an integer of from 1 to 8
• r is an integer of from 1 to 8
• t is an integer of from 1 to 3:
• CF 2 CFO (CF 2 ) q -SO 2 F
• CF 2 CFOCF 2 CF(CF 3 )O(CF 2 ) r
• SO 2 F ii)
• CF 2 CF(OCF 2 CF(CF 3 )) t O(CF 2 ) 2 -SO 2 F (iii)
• the terminal of the polymer is preferably stabilized.
• the polymer electrolyte will be more excellent in stability against hydrogen peroxide or peroxide radicals and thereby has improved durability.
• a method of stabilizing the terminal preferred is a method of copolymerizing a perfluorovinyl compound with another perfluorovinyl compound, followed by fluorination with e.g. fluorine.
• the polymer electrolyte in the present invention may be a polymer having sulfonic acid group, other than a perfluorocarbon polymer having sulfonic acid groups.
• a polymer having such a structure that it has an aromatic ring in the main chain of the polymer or in both the main chain and side chains, and that sulfonic acid groups are introduced to the aromatic ring, and having an ion exchange capacity of from 0.8 to 3.0 meq/g dry resin may be preferably used.
• Specific examples include sulfonated polyarylene, sulfonated polybenzoxazole, sulfonated polybenzothiazole, sulfonated polybenzoimidazole, sulfonated polysulfone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polyphenylene sulfone, sulfonated polyphenylene oxide, sulfonated polyphenylene sulfoxide, sulfonated polyphenylene sulfide, sulfonated polyphenylene sulfide sulfone, sulfonated polyether ketone, sulfonated polyether ether ketone, sulfonated polyether ketone ketone, and sulfonated polyimide.
• the electrolyte membrane of the present invention may contain another component in addition to the polymer electrolyte and the above (a) to (c).
• another component may, for example, be a reinforcing material made of fibers, woven cloth, non-woven cloth or a porous material of a resin such as a polytetrafluoroethylene or a perfluoroalkyl ether.
• a reinforcing material made of fibers, woven cloth, non-woven cloth or a porous material of a resin such as a polytetrafluoroethylene or a perfluoroalkyl ether.
• the electrolyte membrane of the present invention can be obtained by immersing a reinforced electrolyte membrane in a solution containing cerium ions and then incorporating cerium ions and the organic compound (X) in the membrane by the above method (1). Further, the electrolyte membrane of the present invention can be obtained also by a method of preparing a membrane by using a dispersion liquid containing cerium ions, the organic compound (X) and a polymer electrolyte, together with a reinforcing material.
• the present invention further provides a membrane-electrode assembly for a fuel cell, which comprises a layer of the above polymer electrolyte membrane.
• a membrane-electrode assembly is a membrane-electrode assembly for a fuel cell, which comprises a layer of the polymer electrolyte membrane, and a catalyst layer containing a catalyst, an electrically conductive material and an ion exchange resin, provided on both sides of the polymer electrolyte membrane.
• the membrane-electrode assembly further has a gas diffusion layer outside the both catalyst layers.
• the membrane-electrode assembly of the present invention is a membrane-electrode assembly comprising, on both sides of the above electrolyte membrane of the present invention, a catalyst layer containing a catalyst, an electrically conductive material and an ion exchange resin.
• the two catalyst layers function as an anode and a cathode.
• Each of the anode and the cathode of the membrane-electrode assembly preferably has a gas diffusion layer made of a porous electrically conductive sheet outside of each catalyst layer (the side opposite to the membrane).
• the porous electrically conductive sheet is preferably a carbon fiber sheet made of carbon cloth, carbon paper or the like.
• the polymer electrolyte fuel cell usually has such a structure that separators having grooves formed to constitute paths for a fuel gas or an oxidizing agent gas are disposed on both sides of the membrane-electrode assembly, and a plurality of such membrane-electrode assemblies are stacked with the separators to form a stack.
• a hydrogen gas is supplied to the anode side of the polymer electrolyte fuel cell, and an oxygen gas or air is supplied to the cathode.
• a reaction of H 2 ⁇ 2H + +2e - takes place on the anodes, and a reaction of 1/2O 2 +2H + +2e - ⁇ H 2 O on the cathodes, whereby chemical energy is converted to electric energy.
• the electrolyte membrane and the membrane-electrode assembly of the present invention are also applicable to direct methanol fuel cells in which methanol is supplied instead of the fuel gas to the anode side.
• the above-mentioned membrane-electrode assembly may be obtained in accordance with conventional methods, by mixing a catalyst, an electrically conductive material and a solution of an ion exchange resin to obtain a uniform dispersion liquid, and forming a gas diffusion electrode (an electrode having a catalyst layer and a gas diffusion layer stacked) by any of the following methods.
• the catalyst is preferably platinum catalyst fine particles or platinum alloy catalyst fine particles
• the electrically conductive material is preferably a carbon type electrically conductive material such as carbon black.
• the catalyst fine particles are used usually as supported on the electrically conductive material.
• the first method is a method of coating the both surfaces of the electrolyte membrane with the above-mentioned dispersion liquid, drying it, and then attaching two carbon fiber sheets closely onto the both sides.
• the second method is a method of applying the above-mentioned dispersion liquid onto two carbon fiber sheets, drying it, and then placing the two sheets on both sides of the above electrolyte membrane so that the surfaces coated with the dispersion liquid is close in contact with the electrolyte membrane.
• the carbon fiber sheets herein function as gas diffusion layers to more uniformly diffuse the gas to the catalyst-containing layers, and functions as current collectors.
• a substrate separately prepared is coated with the above-mentioned dispersion liquid to make a catalyst layer, such catalyst layers are bonded to an electrolyte membrane by a method such as transcription, then the substrate is peeled off, and the electrolyte membrane is sandwiched between the above-mentioned carbon fiber sheets.
• the ion-exchange resin contained in the catalyst layer is not particularly limited, and it is preferably the above-described perfluorocarbon polymer having sulfonic acid groups.
• the ion-exchange resin in the catalyst layer may contain any one of the above (a) to (c) just like the electrolyte membrane of the present invention.
• an ion-exchange resin containing cerium ions and the organic compound (X) can be applied to both anodes and cathodes, and decomposition of the resin can be effectively suppressed, so as to further enhance the durability of the polymer electrolyte fuel cell.
• any one of the above (a) to (c) may be incorporated after the catalyst layer and the electrolyte membrane are combined.
• ETFE An ethylene/tetrafluoroethylene copolymer
• solution A a uniform liquid (hereinafter referred to as solution A).
• the solid content concentration of solution A was 30 mass%.
• composition C was applied to a 100 ⁇ m ETFE sheet (AFLEX 100N, tradename, manufactured by Asahi Glass Company, Limited) by cast coating with a die coater, preliminarily dried at 80°C for 10 minutes and dried at 120°C for 10 minutes and further annealed at 150°C for 30 minutes to obtain a polymer electrolyte membrane having a thickness of 50 ⁇ m.
• ETFE sheet AFLEX 100N, tradename, manufactured by Asahi Glass Company, Limited
• a membrane having a size of 5 cm ⁇ 5 cm was cut out and left to stand in dry nitrogen for 16 hours, and then the membrane was ashed and subjected to measurement by ICP spectrometry to quantitatively analyze the amount of cerium in the polymer electrolyte membrane for confirmation and as a result, the amount of cerium was 1.5% which corresponds to the addition amount of cerium carbonate hydrate based on the mass of the membrane.
• composition D was applied to a 100 ⁇ m ETFE sheet (AFLEX 100N, tradename, manufactured by Asahi Glass Company, Limited) by cast coating with a die coater, preliminarily dried at 80°C for 10 minutes and dried at 120°C for 10 minutes and further annealed at 150°C for 30 minutes to obtain a polymer electrolyte membrane having a thickness of 50 ⁇ m.
• ETFE sheet AFLEX 100N, tradename, manufactured by Asahi Glass Company, Limited
• This coating fluid E was applied on a substrate film made of polypropylene with a bar coater, and dried in a dryer at 80°C for 30 minutes to prepare a catalyst layer.
• the amount of platinum per unit area contained in the catalyst layer was calculated by measuring the mass of the substrate film alone before formation of a catalyst layer and the mass of the substrate film after formation of the catalyst layer and as a result, it was 0.5 mg/cm 2 .
• the above catalyst layers formed on the substrate film were disposed on both sides of the membrane and transferred by hot press method to obtain a membrane-catalyst layer assembly having an anode catalyst layer and a cathode catalyst layer bonded to both sides of the polymer electrolyte membrane.
• the electrode area was 16 cm 2 .
• This membrane-catalyst layer assembly was interposed between two gas diffusion layers made of carbon cloth having a thickness of 350 ⁇ m to prepare a membrane-electrode assembly, which was assembled into a cell for power generation, and an open circuit voltage test (OCV test) was carried out as an accelerated test.
• OCV test open circuit voltage test
• a membrane-electrode assembly was prepared and assembled into a cell for power generation in the same manner as above, and a durability test under operation conditions under low humidification was carried out.
• the test conditions were as follows. Hydrogen (utilization ratio: 70%)/air (utilization ratio: 40%) was supplied under ambient pressure at a cell temperature of 80°C and at a current density of 0.2 A/cm 2 , and the polymer electrolyte fuel cell was evaluated as to the initial property and durability.
• a membrane-electrode assembly was prepared and assembled into a cell for power generation in the same manner, and a durability test under operation conditions under low humidification at 120°C was carried out.
• the test conditions were as follows. The anode and the cathode were pressurized under 200 kPa, hydrogen (utilization ratio: 50%)/air (utilization ratio: 50%) was supplied at a cell temperature of 120°C and at a current density of 0.2 A/cm 2 , and the polymer electrolyte fuel cell was evaluated as to the initial property and durability.
• uniform transparent liquid composition C prepared in the same manner as in Example 1, 0.73 g of 15-crown-5 manufactured by SIGMA ALDRICH Japan K.K. as a crown ether in an equimolar amount to cerium in the cerium carbonate hydrate was added to the above uniform transparent liquid composition C, followed by stirring at room temperature for 24 hours to obtain uniform transparent liquid composition F. Then, in the same manner as in Example 1, it was found that the total mass of cerium and 15-crown-5 was 3.9% based on the membrane.
• Example 1 a polymer electrolyte membrane having a thickness of 50 ⁇ m was prepared in the same manner as in Example 1 except that the above liquid composition F was used, and electrode layers were bonded to the membrane in the same manner as in Example 1 to prepare a membrane-electrode assembly, and the same evaluations as in Example 1 were carried out.
• Tables 1 to 4 The results are shown in Tables 1 to 4.
• an ion exchange membrane having a thickness of 50 ⁇ m, made of a perfluorocarbon polymer having sulfonic acid groups (ion exchange capacity: 1.1 meq/g dry resin) in a size of 5 cm x 5 cm (area: 25 cm 2 ) was used.
• the weight of the entire membrane after left to stand in dry nitrogen for 16 hours was measured in dry nitrogen and was 0.251 g.
• cerium(III) nitrate (Ce(NO 3 ) 3 ⁇ 6H 2 O) was dissolved in 500 ml of distilled water so that cerium ions (trivalent) in an amount corresponding to 60% of the amount of sulfonic acid groups in the membrane were contained, and the above ion exchange membrane was immersed in the solution, followed by stirring with a stirrer at room temperature for 40 hours so that part of sulfonic acid groups in the ion exchange membrane were ion-exchanged with cerium ions.
• the cerium(III) nitrate solution before and after the immersion was analyzed by ion chromatography and as a result, the ion exchange rate of the ion exchange membrane with cerium ions (the ratio of -SO 3 - groups exchanged with cerium ions to the total number of -SO 3 - groups originally present in the membrane) was found to be 58%.
• the cerium content in the membrane was 2.94 mass%.
• the membrane was immersed in a 1 mol/L phosphoric acid aqueous solution at room temperature for 60 hours and as a result, precipitation of cerium phosphate in the membrane was confirmed by X-ray diffraction. Then, using the membrane, electrode layers were bonded to the membrane in the same manner as in Example 1 to prepare a membrane-electrode assembly, and the same evaluations as in Example 1 were carried out. The results are shown in Tables 1 to 4.
• composition F 100 g of solution A and 0.87 g of 18-crown-6 manufactured by SIGMA ALDRICH Japan K.K. were charged into a 300 ml round-bottomed flask made of glass and stirred at room temperature for 24 hours by a meniscus blade made of PTFE to obtain uniform transparent liquid composition F.
• the obtained composition F was applied to a 100 ⁇ m ETFE sheet (AFLEX 100N, tradename, manufactured by Asahi Glass Company, Limited) by cast coating with a die coater, preliminarily dried at 80°C for 10 minutes and dried at 120°C for 10 minutes and further annealed at 150°C for 30 minutes to obtain a polymer electrolyte membrane having a thickness of 50 ⁇ m.
• ETFE sheet AFLEX 100N, tradename, manufactured by Asahi Glass Company, Limited
• Example 2 Using, as a polymer electrolyte membrane, the same ion exchange membrane as used in Example 3 without any treatment, a membrane-electrode assembly was prepared in the same manner as in Example 1. With respect to the membrane-electrode assembly, the same evaluations as in Example 1 were carried out. The results are shown in Tables 1 to 4.
• the electrolyte membrane of the present invention is very excellent in durability against hydrogen peroxide or peroxide radicals formed by power generation of a fuel cell. Accordingly, a polymer electrolyte fuel cell provided with a membrane-electrode assembly having the electrolyte membrane of the present invention has durability over a long period of time either in power generation under low humidification and in power generation under high humidification.

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